OT: Big rig trucks: why air brakes and not electric brakes - Page 3
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  1. #41
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    Quote Originally Posted by EPAIII View Post

    Somewhere along the line, probably due to some accidents caused by those tanks leaking down and the brakes releasing, they reversed the way the actual brake mechanism worked. Air pressure in the line still releases them, but unless I am mistaken, they now used springs to set the brakes and the air to release them. The tank on each car either went away or became a lot less important for safety.
    No springs. That is a truck phenomenon. Not sure what it is for other than allowing the tractor to couple without airing up the trailer first. Last year, at Field B.C. on the Canadian Pacific, train 301 experienced brake problems in mountainous territory and went into emergency, so that the train was stopped by the air in the reservoirs on each car. Normal procedure is to immediately start setting hand brakes before the air can leak off. A releif crew arrived and found no handbrakes set. They boarded the train which began to roll away and inexplicably, they stayed aboard. result: 3 men dead in the locomotive upside down in the Kicking Horse river and 99 grain hoppers destroyed, many in tunnels. Why this happened seems to be being covered up but the facts are that the only two ways to hold that train are the residual air in the reservoirs, which is quite temporary at 60 below, and hand brakes.

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    I have not seen any replies that make clear that there are two separate air brake systems on heavy duty trucks; service brakes and parking brakes.

    The parking brakes are also called spring brakes. They are not used on the front (steering) axle. They are actuated by large coil compression springs that apply force to the cams or wedges on the drum brakes on the truck's rear and trailer axles. The springs do not modulate, they are either fully on or off if the system pressure is normal. The parking brakes are released by applying air pressure to compress the springs. If the air is released by the driver or by accident, the brakes will be applied. These are parking brakes, not meant for use during normal driving. They are operated by a knob on the instrument panel.

    The service brakes are for use while driving and are controlled by the driver's foot and use air chambers separate from the parking brake chambers. The service brake chambers directly apply force to the cams or wedges on the brake drums, or to disc calipers. The braking force is modulated by air pressure, directly controlled by the foot valve's pedal position.

    Larry,

    who has pretty much forgotten what a truck is, but still has some memories.

  3. Likes jmead, tdmidget, Tci_ liked this post
  4. #43
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    Quote Originally Posted by tdmidget View Post
    ... train 301 experienced brake problems in mountainous territory and went into emergency, so that the train was stopped by the air in the reservoirs on each car.
    The way train brakes work has always ruined the end of Silver Streak for me

  5. #44
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    Quote Originally Posted by gustafson View Post
    When air brakes came out a 40 amp [automotive] generator was big. In order to have power off brakes you need the power to retract the spring that drives the brakes at full power. One would have to do some math but I think that would be quite some current

    Then there is the issue of voltage drop over long distances. Some trains in the US are as much a two miles long. It would be difficult to provide electrical power to the whole train, whereas air pressure carries out nicely to the very last car and can be provided from an air compressor located in the locomotive.

    Air brakes have been the standard for railroads at least for over 150 years and they seem to work very well. .

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    Quote Originally Posted by EmanuelGoldstein View Post
    The way train brakes work has always ruined the end of Silver Streak for me

    In order properly to enjoy a drama it's necessary, at least for a period of time, to suspend one's disbelief.

  7. #46
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    Quote Originally Posted by EmanuelGoldstein View Post
    You have to push pretty hard but ...

    Attachment 281110
    That is where my forks and front wheel came from! Harley was selling off a mess of road race bikes and parts, it's a bit fuzzy but it must have been about '76 or so. I was short of cash but had enough for the forks and wheel, both brand new for about 150.00 if I remember correctly.

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    Quote Originally Posted by Scottl View Post

    PS: As for bikes I wouldn't trade the simplicity and predictability of disk brakes for "the good old days". 2 up front and one rear make for very efficient stopping, especially when multi-piston calipers are used.
    My 500cc Triumph only weighs about 285 lbs so that 330mm 4LS Fontana brake is not overworked. I have a Slippery Sam replica Triumph Trident as well, It has 3 alloy Lockheed calipers on it. at 420 lbs it is a bit of a tank but stops on a dime with those brakes.

  9. #48
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    Quote Originally Posted by moonlight machine View Post
    My 500cc Triumph only weighs about 285 lbs so that 330mm 4LS Fontana brake is not overworked. I have a Slippery Sam replica Triumph Trident as well, It has 3 alloy Lockheed calipers on it. at 420 lbs it is a bit of a tank but stops on a dime with those brakes.
    A bit of a tank? Try stopping a high horsepower Harley. What worked for me was 2 iron disks up front and one in the rear with high friction pads and steel braid lines for better response and feel. One mod that was popular with some Harley guys a few years ago was to get junkyard Tokico multi-piston calipers off a Susuki Katana and mount them with custom brackets on the front. The hard-core lifestyle guys would grind the Tokico logo off and repaint the calipers but others left it on as a "who gives a f***, whatever works" statement. The calipers were of course overhauled before using them. The calipers were easy to come by as a lot of novices wrecked Katanas without harming the calipers.

  10. #49
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    Quote Originally Posted by Scottl View Post
    A bit of a tank? Try stopping a high horsepower Harley. What worked for me was 2 iron disks up front and one in the rear with high friction pads and steel braid lines for better response and feel. One mod that was popular with some Harley guys a few years ago was to get junkyard Tokico multi-piston calipers off a Susuki Katana and mount them with custom brackets on the front. The hard-core lifestyle guys would grind the Tokico logo off and repaint the calipers but others left it on as a "who gives a f***, whatever works" statement. The calipers were of course overhauled before using them. The calipers were easy to come by as a lot of novices wrecked Katanas without harming the calipers.
    What does that Harley weigh, 750-800 lbs? None for me thanks, you might as well have a car.

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    Quote Originally Posted by moonlight machine View Post
    I have not noticed that in the past, Next time I ride it I'll check them. Thanks for the tip.
    If the spokes hit the rim at a tangent, hub dimension does not affect spoke tension.

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    So can we have electric motorsickle brakes, made by "Lucas Electric" ?....

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    Digger, are you trying to say that Lucas Electric was not a world class supplier?

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    Quote Originally Posted by CarbideBob View Post
    Digger, are you trying to say that Lucas Electric was not a world class supplier?
    It's popular to run down Lucas but I can say for certain that I have been on the side of the road only once in the hundred or more thousand miles I have ridden British bikes. The power wire to the coils broke right by the second crimp at the blade terminal. 1969 BSA Lightning 650. Took all of about 5 minutes of trouble shooting to find the trouble, and about a minute to strip back the insulation, fold the wire over the terminal and push the wire terminal on over the wire. One kick and we are on the road again. Lucas is much better than the crap they put on italian bikes.

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    Quote Originally Posted by jim rozen View Post
    If the spokes hit the rim at a tangent, hub dimension does not affect spoke tension.
    Well they definitely are on a tangent!

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    so fundamentally an electric solenoid can only exert a maximum force of about 100 psi due to the saturation flux density of 2T, and the practical size of the coil needed to get low losses at that pressure is too large to even consider.

    rather than a mechanical multipler such as a drum brake with an extra lever attached so you could have say, 6 inches of travel on the solenoid instead of a quarter inch with a hydraulic system, you could instead use a multiplate clutch brake. minimum required would be something like 5 disks and 6 break pads. still need a fail safe such as a back up hydraulic system, which could be incorporated into the solenoid.

  17. #56
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    Quote Originally Posted by moonlight machine View Post
    It's popular to run down Lucas but I can say for certain that I have been on the side of the road only once in the hundred or more thousand miles I have ridden British bikes. The power wire to the coils broke right by the second crimp at the blade terminal. 1969 BSA Lightning 650. Took all of about 5 minutes of trouble shooting to find the trouble, and about a minute to strip back the insulation, fold the wire over the terminal and push the wire terminal on over the wire. One kick and we are on the road again. Lucas is much better than the crap they put on italian bikes.
    In my motorcycling days I owned about 40 motorcycles. 8 of them were British: 3 BSA's, 2 Matchless, 2 AJS and one Triumph. All had Lucas electrics, generators and magnetos. The magnetos were OK generally but the lights were only so-so. There was a saying: Lucas lights are like the sun and when the motor drops to an idle, the sun sets. "

    I had a BSA Racing bike where the rotor in the magneto would get wet from condensation and the result was weak spark. I finally disassembled it and baked the rotor in an oven and dried it out. I then coated it with epoxy and it worked fine after that.

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    There is no electric power when the system goes to shit.
    Nothing, zero zip.
    That is deal behind the system. Fail safe. Not fail maybe, not I hope there is battery.
    This is why it works, no power... stop. This sometimes leads to skid marks you see on the freeway that seem weird and go off to the side. Exciting.
    And by the way your computer anti lock brakes still work, they are not electric brakes. It is a module in between and it will shut down if the computer and it are not happy.
    Bob

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    The most effective electric brake ever put on trucks was the old "Telma Retarder"....the things were fantastic,especially in the days when most truck brakes were undersized....Eddy current braking, self cooling ,and using no more than a few amps of current from the batteries.

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    The original Le Tourneau electric wheels had electric brakes using multiple discs ,like a multiplate clutch.

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    Quote Originally Posted by john.k View Post
    The most effective electric brake ever put on trucks was the old "Telma Retarder"....the things were fantastic,especially in the days when most truck brakes were undersized....Eddy current braking, self cooling ,and using no more than a few amps of current from the batteries.
    They are still in business, they are used in dynamometers as well.


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